Pyrolytic vacuum deposition from gases



March 11, 1969 R. J. DIEFENDORF' 3,432,330

PYROLYTIC VACUUM DEPOSITION FROM GASES Filed April 25, 1961 /-//'sAttorney.

United States Patent 3,432 330 PYROLYTIC VACUUM DEPOSITION FROM GASESRussell J. Diefendorf, Schenectady, N.Y., assignor to This inventionrelates to methods of forming articles and coatings and moreparticularly to methods of forming pyrolytic articles and coatings.

Pyrolytic articles and coatings are defined as materials made from gasesby thermal decomposition or from materials by evaporation and depositionon a surface. In pyrolytic materials, planar crystallites are arrangedso that their layer structures are parallel to the deposition surface.These materials are useful in high temperature environments. Developmentof missile and space propulsion systems has created an additionalrequirement for pyrolytic components in these systems.

carbonaceous gases have been thermally decomposed and deposited on asurface to produce pyrolytic graphite. As a result of the decomposition,carbon is removed from the gas and deposits on the surface so thatplanar graphite crystallites are aligned into a layer structure. Itwould be desirable to provide other pyrolytic articles and coatings forhigh temperature application. It would also be advantageous to providepyrolytic articles and coatings with high electrical resistance.

It is an object of my invention to provide a deposition method offorming pyrolytic articles.

It is another object of my invention to provide a deposition method offorming pyrolytic coatings.

It is a further object of my invention to provide a deposition method offorming pyrolytic articles and coatings having high electricalresistance.

In carrying out my invention in one form, a deposition method comprisesproviding a chamber, providing a deposition surface in the chamber,heating the chamber to a temperature in the range of 1,400 C. to 2,000C., and flowing a mixture of boron, carbon, and nitrogen through thechamber whereby pyrolytic material is formed on the surface.

These and various other objects, features and advantages of theinvention will be better understood from the following description takenin connection with the accompanying drawing in which:

FIGURE 1 is a sectional view of a deposition apparatus for formingpyrolytic articles and coatings in accordance with my invention;

FIGURE 2 is a sectional view of a modified deposition apparatus; and

FIGURE 3 is a sectional view of another modified deposition apparatus.

In FIGURE 1 of the drawing, a deposition apparatus shown generally atcomprises a brass chamber 11 including a cylindrical body portion 12 andend closure plates 13. A flange 14 is located at each end of bodyportion 12 to which an associated plate 13 is fastened by means of bolts15 extending through apertures in both the flange and plate. In one endplate 13, an aperture 16 is located in which a tube 17 is positioned andextended to a pump 18 for evacuating chamber 11. A window 19 is locatedin body portion 12 to view the operation. A pair of spaced water-cooled,brass electrodes 20 are positioned within chamber 11. An electrical lead21 is secured to each electrode 20 and to a suitable alternating currentpower source (not shown) to heat the electrodes to a temperature in therange of 1,400" C. to 2,000 C. Each electrode 20 has a supporting fin 22attached thereto, which fins support a graphite member 23 therebetween.A deposit 24 of Patented Mar. 11, 1969 "ice pyrolytic material is shownon member 23. A water chamber 25 surrounds each end of chamber 11 and isprovided with a water inlet line 26 and water outline line 27. An airnozzle 28 cools the central portion of chamber 11. A container 29 ispositioned within chamber 11 to hold materials containing boron andnitrogen, boron and carbon, or nitrogen and carbon components. An inletline 30, which is connected to chamber 11, supplies a materialcontaining a boron, carbon or nitrogen component which is not providedin container 29.

In FIGURE 2 of the drawing, a modified deposition apparatus is shownwhich is identical to the apparatus of FIGURE 1 except that anadditional inlet line 31 is connected to chamber 11. In the apparatus ofFIGURE 2, one material containing a boron, carbon or nitrogen componentis held in container 29 while inlet lines 30 and 31 supply the remainingmaterials containing the additional components to provide a mixture ofboron, carbon and nitrogen.

In FIGURE 3 of the drawing, another modified deposition apparatus isshown which comprises a chamber 11 having a cylindrical body portion 12with end closure plates 13. A flange 14 is located on each end of bodyportion 12 to which an associated plate 13 is fastened by means of bolts15 extending through apertures in both the flange and plate. Awater-cooled electrode 32 is positioned adjacent each end plate andfastened by means of bolts 15 around its outer periphery between flange14 and plate 13. Electrodes 32 support an inner chamber 33 in the formof a raphite tube concentrically within chamber 11. In one end plate 13,an aperture 16 is located in alignment with the outlet end of innerchamber 33. Tube 17 is positioned in aperture 16 and connected to pump18 for evacuating chamber 11. An aperture 34 is located in the oppositeend plate in alignment with the inlet end of inner chamber 33. A closure35 covers aperture 34 and is provided with two apertures through whichinlet lines 36 and 37 extend to connect with inner chamber 33. Inletlines 36 and 37 furnish materials containing boron, carbon and nitrogencomponents to the inner chamber. Electrodes 32 heat chamber 33 to atemperature in the range of 1,400" C. to 2,000 C. Water-cooling coils 38surround the outer surface of chamber 11.

I discovered unexpectedly that pyrolytic articles and coatings wereformed with high electrical resistance by providing a deposition surfacein a chamber, heating the chamber to a temperature in the range of 1,400C. to 2,000 C., and flowing a mixture of boron, carbon and nitrogenthrough the chamber. The preferred chamber pressure is in the range of0.05 millimeter of mercury to 3 centimeters of mercury. I found thatmaterials containing boron, carbon and nitrogen components which can beemployed in my deposition method include trimethylborate, borontrichloride, nitrogen, ammonia, methane, B- trichlorborazole, anddiethylamine. Trimethylborate, methane and diethylamine provide thecarbon component. Boron trichloride, B-trichlorborazole, andtrimethylborate produce the boron component. Nitrogen and ammoniaprovide the nitrogen component.

In the operation of the deposition apparatus in FIG- URE 1, a materialcontaining boron and carbon, boron and nitrogen, or nitrogen and carboncomponents, isplaced in container 29 and the chamber is evacuated to apressure in the range of 0.05 millimeter of mercury to 3 centimeters ofmercury. Power is supplied to leads 21 to heat watercooled electrodes 20to a temperature in the range of 1,4-00 C. to 2,000 C. Member 23 ofgraphite is heated by electrodes 20 and associated fins 22 to thistemperature range. The material in container 29 contains two componentsof the required three components of boron, carbon and nitrogen whileinlet line 30 supplies the third component. For example,trimethylborate, a liquid, is placed in container 29 to provide thecarbon and boron components while ammonia is supplied through inlet line30 to provide the nitrogen component. When member 23 is heated to atemperature in the range of 1,400 C. to 2,000 O, a mixture of boron,carbon and nitrogen forms which flows through the chamber and depositson this member as a pyrolytic material. Pump 18 maintains a low pressurein chamber 11 while it removes the products of the reaction therefrom.

The operation of the deposition apparatus in FIGURE 2 is identical withthe operation of the apparatus in FIG- URE 1 except that three materialsare provided in container 29, and through inlet line 30 and 31,respectively, to provide the mixture of boron, carbon and nitrogen. Forexample, diethylamine is placed in container 29, ammonia is fed throughline 30 and boron trichloride is fed through line 31. When member 23 isheated to a temperature in the range of 1,400 C. to 2,000 C., a mixtureof boron, carbon and nitrogen forms which flows through the chamber anddeposits on this member as a pyrolytic material.

In the operation of the deposition chamber in FIGURE 3, power issupplied through leads (not shown) to heat water-cooled electrodes 32and inner chamber 33 to a temperature in the range of 1,400 C. to 2,000C. Chamber 33 is evacuated to a pressure in the range of 0.05 millimeterof mercury to 3 centimeters of mercury. A material containing boron andcarbon, boron and nitrogen, or nitrogen and carbon components issupplied through inlet line 36 to chamber 33. A material containing thethird component is supplied through inlet line 37 to chamber 33. Forexample, B-trichlorborazole is heated to 80 C. and supplied throughinlet line 36 to provide the boron and nitrogen components while methaneis supplied through inlet line 37 to provide the carbon component. Amixture of boron, carbon and nitrogen forms which flows through chamber33 and deposits on the interior surface thereof as a pyrolytic material.Pump 18 maintains a low pressure in the chamber while it removes thereaction products.

It will be understood that the interior surface of the chamber or aportion thereof can be employed as a deposition surface. Furthermore,three inlets can be employed to feed the materials containing boron,carbon and nitrogen components to chamber 11. If it is desired, all thematerials can be placed within one or more containers within chamber 11.

Several examples of pyrolytic material which were made in accordancewith the methods of the present invention are as follows:

EXAMPLE I A deposition apparatus was set up in accordance with FIGURE 1of the drawing wherein a 4% inch diameter cylindrical brass chamberhaving a length of 8 inches was provided with end closure plates. A pairof watercooled brass electrodes with fins supported a graphite memberhaving end diameters of %32 inch and a one-inch reduced center portionhaving a diameter of 6 inch. The ends of the chamber were water-cooledwhile the center portion was air-cooled. Trimethylborate was placed in acontainer which was positioned in chamber 11 to provide the carbon andboron components. The chamber was closed and evacuated. Power wassupplied through the electrodes and heated the member to a temperatureof 1,650 C. at its reduced center portion. Ammonia was fed to thechamber through an inlet line to provide the nitrogen component. Themember was heated for one minute, during which time the pressure rose toabout centimeters of mercury. A mixture of boron, carbon and nitrogenwas formed which flowed through the chamber and deposited as pyrolyticmaterial on the center portion of the graphite member. The pyrolyticmaterial exhibited a resistance of 0.008 ohm centimeter along thesurface of the deposit.

4 EXAMPLE II A deposition apparatus was set up in accordance with FIGURE2 of the drawing wherein a 4% inch diameter cylindrical brass chamberhaving a length of 8 inches was provided with end closure plates. A pairof water-cooled brass electrodes with fins supported a graphite memberhaving an end diameter of inch and a one-inch reduced center portionhaving a diameter of inch. The ends of the chamber were water-cooledwhile the center portion was air-cooled. Diethylamine was placed in acontainer which was positioned in chamber 11 to provide the carboncomponent. The chamber was closed and evacuted. Power was suppliedthrough the electrodes and heated the member to a temperature of l,650C. at its reduced center portion. Ammonia was fed to the chamber throughan inlet line to provide the nitrogen component. Boron trichloride wasfed to the chamber through a second inlet line to provide the boroncomponent. The member was heated for about one minute. A mixture ofboron, carbon and nitrogen was formed which flowed through the chamberand deposited as pyrolytic material on the center portion of thegraphite member. The pyrolytic material exhibited a resistance of 40.0megohm centimeters along the surface of the deposit.

EXAMPLE III A deposition apparatus was set up generally in accordancewith FIGURE 3 of the drawing. The inner chamber in the form of agraphite tube furnace had a diameter of 1 inch and a length of 7 inches.The exterior surface of the outer chamber was provided with coils towater-cool the tube furnace. Power was supplied through leads to heatthe water-cooled electrodes and inner chamber to a temperature of 1,500C. along the tube. The chamber was evacuated to a pressure of 0.05 mm.of mercury. B-trichlorborazole was heated to a temperature of C. andsupplied to an inlet line to the inner chamber to provide the boron andnitrogen components. Methane was supplied at a rate of 1 cubic foot perhour to the inlet line to the inner chamber to provide the carboncomponent. The inner chamber was heated for about four hours. A mixtureof boron, carbon, and nitrogen was formed which flowed through the innerchamber and deposited as pyrolytic material on the inner surface of thechamber tube. The pyrolytic material exhibited a resistance of 2.0 ohmcentimeters along the surface of the deposit.

While other modifications of this invention and variations of methodwhich may be employed within the scope of the invention have not beendescribed, the invention is intended to include such that may beembraced within the following claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A deposition method which comprises providing a chamber, providing adeposition surface in said chamber, evacuating said chamber to apressure in the range of 0.05 millimeter of mercury to 3 centimeters ofmercury, heating said chamber to a temperature in the range of l,400 C.to 2,000 0, providing a mixture of boron, carbon and nitrogen frommaterials containing boron, carbon and nitrogen, and flowing saidmixture through said chamber whereby pyrolytic material is deposited onsaid surface.

2. A deposition method which comprises providing a chamber, providing adeposition surface in said chamber, evacuating said chamber to apressure in the range of 0.05 millimeter of mercury to 3 centimeters ofmercury, heating said surface to a temperature in the range of l,400 C.to 2,000 C., providing a mixture of boron, carbon and nitrogen frommaterials containing boron, carbon and nitrogen, and flowing saidmixture through said chamber whereby pyrolytic material is deposited onsaid surface.

3. A deposition method which comprises providing a chamber, positioningat least one member in said chamber, evacuating said chamber to apressure in the range of 0.05 millimeter of mercury to 3 centimeters ofmercury, heating said chamber to a temperature in the range of l,400 C.to 2,000 C., providing a mixture of boron, carbon and nitrogen frommaterials containing boron, carbon and nitrogen, and flowing saidmixture through said chamber whereby pyrolytic material is deposited onsaid member.

4. A deposition method which comprises providing a chamber, positioningat least one member in said chamber, evacuating said chamber to apressure in the range of 0.05 millimeter of mercury to 3 centimeters ofmercury, heating said member to a temperature in the range of "l,400 C.to 2,000 O, providing a mixture of boron, carbon and nitrogen frommaterials containing boron, carbon and nitrogen, and flowing saidmixture through said chamber whereby pyrolytic material is deposited onsaid member.

5. A deposition method which comprises providing a chamber, positioningat least one member in said chamber, evacuating said chamber to apressure in the range of 0.05 millimeter of mercury to 3 centimeters ofmercury, feeding materials containing boron, carbon and nitrogencomponents to said chamber, heating said chamber to a temperature in therange of 1,400" C. to 2,000 C. to provide a mixture of boron, carbon andnitrogen, and flowing said mixture through said chamber wherebypyrolytic material is deposited on said member.

6. A deposition method which comprises providing a chamber, positioningat least one member in said chamber, evacuating said chamber to apressure in the range of 0.05 millimeter of mercury to 3 centimeters ofmercury, feeding materials containing boron, carbon and nitrogencomponents to said chamber, heating said member to a temperature in therange of 1,400 C. to 2,000 C. to provide a mixture of boron, carbon andnitrogen, and flowing said mixture through said chamber wherebypyrolytic material is deposited on said member.

7. A deposition method which comprises providing a chamber, positioningat least one member in said chamber, evacuating said chamber to apressure in the range of 0.05 millimeter of mercury to 3 centimeters ofmercury, providing materials containing boron, carbon and nitrogencomponents within said chamber, heating said chamber to a temperature inthe range of 1,400 C. to 2,000 C. to provide a mixture of boron, carbonand nitrogen, and flowing said mixture through said chamber wherebypyrolytic material is deposited on said member.

8. A deposition rnethod which comprises providing a chamber, positioningat least one member in said chamber, evacuating said chamber to apressure in the range of 0.05 millimeter of mercury to 3 centimeters ofmercury, providing materials containing boron, carbon and nitrogencomponents within said chamber, heating said member to a temperature inthe range of 1,400 C. to 2,000 C. to provide a mixture of boron, carbonand nitrogen, and flowing said mixture through said chamber wherebypyrolytic material is deposited on said member.

9. The process of producing an alloy comprising pyrolytic graphite andboron which comprises cont-acting a gaseous hydrocarbon and borontrichloride at a temperature between about 1,500 C. and 2,000 C. and apressure below about 20 mm. of mercury.

10. The process of producing an alloy comprising pyrolytic graphite andboron which comprises contacting methane and boron trichloride at atemperature between about 1,500 C. and 2,000 C. and a pressure belowabout 20 mm. of mercury.

References Cited UNITED STATES PATENTS 2,405,449 8/1946 Robinson et a1.117226 X 2,853,969 9/1958 Drewett 117--46 2,200,521 5/ 1940 Siegel117-46 2,764,510 9/1956 Ziegler 117-216 2,810,365 10/1957 Keser 118472,810,664 10/ 1957 Gentner 1l7--226 RALPH S. KENDALL, Primary Examiner.

A. GOLIAN, Assistant Examiner.

US. Cl. X.R. 117-106, 121

1. A DEPOSITION METHOD WHICH COMPRISES PROVIDING A CHAMBER, PROVIDING ADEPOSITIONSURFACE IN SAID CHAMBER, EVACUATING SAID CHAMBER TO A PRESSUREIN THE RANGE OF 0.05 MILLIMETER OF MERCURY TO 3 CENTIMETERS OF MERCURY,HEATING SAID CHAMBER TO A TEMPERATURE IN THE RANGE OF 1,400*C. TO2,000*C., PROVIDING A MIXTURE OF BORON, CARBONAND NITROGEN FROMMATERIALS CONTAINING BORON, CARBONAND NITROGEN, AND FLOWING SAID MIXTURETHROUGH SAID CHAMBER WHEREBY PYROLYTIC MATERIAL IS DEPOSITED ON THESURFACE.